"twelfth and last (by modern reckoning) month of the calendar, the month of the winter solstice," late Old English, from Old French decembre, from Latin December, from decem "ten" (from PIE root *dekm- "ten"); tenth month of the old Roman calendar, which began with March.

The -ber in four Latin month names is probably from -bris, an adjectival suffix. Tucker thinks that the first five months were named for their positions in the agricultural cycle, and "after the gathering in of the crops, the months were merely numbered."

If the word contains an element related to mensis, we must assume a *decemo-membris (from *-mensris). October must then be by analogy from a false division Sep-tem-ber &c. Perhaps, however, from *de-cem(o)-mr-is, i.e. "forming the tenth part or division," from *mer- ..., while October = *octuo-mr-is. [T.G. Tucker, "Etymological Dictionary of Latin"]

Decembrist, in Russian history in reference to the insurrection against Nicholas I in December 1825, is by 1868 in English, translating Russian dekabrist, from dekabr' "December."

"headband with two springs carrying ornaments," 1982, trademark name held by Ace Novelty Company. Earlier it had been a patent name for a type of building blocks, manufactured 1969-1973.

satellite of Mars, discovered in 1877, named for Greek deimos, literally "fear, terror," also, as Deimos, the personification of such, regarded as a son of Ares, twin brother of Phobos"fear, panic, flight" (for which see phobia). Greek deimos is from PIE *duei- "fear," source also of Sanskrit dvesti "hate," Avestan duuaetha "threat," and possibly Latin dirus "fearful."

U.S. state, river, and native tribe, all named for the bay, which was named for Baron (commonly "Lord") De la Warr (Thomas West, 1577-1618), first English colonial governor of Virginia. The family name is attested from 1201, from Delaware in Brasted, Kent, which is probably ultimately from de la werre "of the war" (a warrior), from Old French werre/guerre "war" (see war (n.)).  Related: Delawarean.

town in Holland,named from its chief canal, from Dutch delf, literally "ditch, canal;" which is related to Old English dælf and modern delve. As a short form of delftware, attested from 1714.

1620s, "of Delos," the tiny island in the Aegean that was the reputed birthplace of Apollo and Artemis. Delian problem "find the length of the side of a cube having double the volume of a given cube," was set by the oracle at Delos when it answered (430 B.C.E.) that the plague in Athens would end when Apollo's (cube-shaped) altar was doubled. The Latin fem. form of the word became the proper name Delia.

"temptress, treacherous lover," 1590s, from the name of the woman who seduced and betrayed Samson in Judges, from Hebrew Delilah, literally "delicate, languishing, amorous," from Semitic root d-l-l "to hang down, to languish."

1796, from Italian Accademia della Crusca, literally "Academy of the Chaff," "the name of an Academy established at Florence in 1582, mainly with the object of sifting and purifying the Italian language; whence its name, and its emblem, a sieve" [OED]. From della "of the" (from Latin de "of" + illa "that") + crusca "bran." Related: Della-Cruscan.

1787, from name of a family of 15c. Florentine painters and sculptors; used of wares made by Luca Della Robbia (1400-1482), or those like them.

trademark name, by 1942; originally a morphine substitute.